INT 2F - DOS 4+ APPEND - SET RETURN FOUND NAME STATE
        AX = B711h
Note:   if the next INT 21h call (and ONLY the next) is function 3Dh, 43h, or
        6Ch (also 4B03h and 4Eh if /X active), the fully qualified filename is
        written over top of the filename passed to the INT 21h call.  The
        application must provide a sufficiently large buffer.  This state is
        reset after the next INT 21h call processed by APPEND.
BUG:    DOS 4.0 APPEND reportedly overwrites DS:DX instead of DS:SI for
          INT 21/AH=6Ch